Photoelectric inspection device



June 1, 1948. H w, H M N ETAL 2,442,690

PHOTOELECTRIC INSPECTION DEVICE Filed Sept. 6, 1943 4 Sheets-Sheet 1 LI L2 PHGTOC EL L FRAME RZLI loo JTATION STATION LONG/TUD/NAL SECTION T/IEU PHOTOCEL FE/IME ATANYSTAT/ON. is

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PHOTOELECTRIC INSPECTION DEVICE Filed Sept. 6, 1945 4 Sheets-Sheet 2 I7 TE/INJVEESE 55c T/ON THRU PHOTO CELL FRAME ATANYJTATION /VVENT0$ Mme) I/V/LLMMflaFFMA/v 6,20 VEB /7'. #51. MER

Jfud, M MW June 1948- H. w. HOFFMAN ETAL PHOTOELECTRIC INSPECTION DEVICE Fi led Sept. 6, 1943 4 Sheets-Sheet 5 Patented June 1, 1948 PHOTOELECTRIC INSPECTION DEVICE Harry William Hoffman, Anoka, and Grover H.

Helmer, Minneapolis, Minn., asslgnors to Federal Cartridge Corporation, Minneapolis, Minn., a corporation of Minnesota Application September 6, 1943, Serial No. 501,424

10 Claims. 1

This invention relates to an apparatus for accurately and automatically indicating and recording movements of illuminated or light-reflective bodies past a station or plurality of stations in succession, and particularly to sensitive photo-electric apparatus for indicating and recording the operation of illuminated projectiles.

The invention has particular applicability where it is desired to indicate and record the performance of illuminated or illuminatible and reflective bodies in their movement past one or more stations. It is, therefore, an object of the invention to provide such an apparatus for indicating and recording the movement of Projectiles, and particularly by photo-electric means. It is also an object of the invention to provide a photo-electric viewing and amplifying apparatus together with indicating or recording apparatus-of extreme sensitivity capable of being operated by exceedingly small changes in light density during instantaneous periods, and particularly to provide such an apparatus capable of use where the available power supply is relatively poorly regulated and is subject to frequent instantaneous variations in voltage.

Other and further objects of the invention are those inherent and implied by the apparatus herein described and claimed.

Throughout the drawings, corresponding numera s denote corresponding parts. The apparatus is illustrated with respect to the drawings in which Figure 1 is a schematic plan or elevational view of the entire system. Figure 2 is a sectional view through one of the photo-electric stations shown at Figure 1 and taken in the direction of arrows 2-2 of Figure 1. Figure 3 is a longitudinal, sectional view through either of the photoelectric cell statlons of the system and taken in the direction of arrows 3-3 of Figure 2. Figure 4 is a front, elevational view of one of the photoelectric devices of Figure 2 taken in the direction of arrows 4--4 of Figure 2. Figure 5 is an electrical wiring diagram of an amplifier circuit such as is used in each photo-electric station.

Figure 6 is a wiring diagram together with a schematie representation of the recorder apparatus of the system. Figure 7 is an elevational view, partly in section, of a portion of the recording apparatus.

Referring to Figure 1, there is illustrated a range generally designated I0, along which an object such as a projectile is adapted to pass as, for example, along the path of line ||--|2. At one or more places along the range there are established stations for indicating and providing responsive electrical signals as a result of the passage of a projectile or other object past the station. Thus, along the range Ill there are illustrated station and station 2, although it will be understood that in other installations it may be desirable to use more than two stations depending upon the work to be done.

Stations I and 2 and any additional stations which may be utilized in the system are preferably of identical construction and each includes a photo-electric cell frame generally designated I5, having the general configuration illustrated in Figures 2, 3 and 4, although, obviously, this mechanical framework may be widely varied in accordance with the particular installation. For purposes of illustration herein it is assumed that it is desired to record the passage past stations I and 2 of an illuminated or illuminatible projectile, and that the projectile is moving at gunfire velocity. In such a system the photo-electric cells are conveniently housed in a framework generally designated l5, having top members l6, bottom members I! and side members I8 and I9, defining the cross-sectional space of the range through any portion of which the projectile may pass. Adjacent to the side member l9 there are positioned a plurality of photo-electric cell-enclosing boxes generally designated 2|, 22, 23, 24, 25 and 26 of generally similar, but not identical construction. Thus, in the specific embodiment illustrated, there are six boxes, 2| and 26 being identical, 22 and 25 being identical, and 23 and 24 being identical. However, the boxes 2|, 22

and 23 are arranged in transposed position with respect to boxes 24, 25 and 25. More specifically it will be noted that box 2| has top and bottom walls 30 and 3| which extend forwardly to the vertical wall IS. The vertical wall I9 is composed of one or more vertically spaced panels, having a space therebetween so as to form a vertical iewing aperture as illustrated at the bracket 32 in Figure 3.

Within the box 2| there are a plurality of baflles 33, 34, 35 and 36, each of which has an opening cut centrally therein. The openings of the several baflles are chamfered at the edge toward the right in Figure 2; (i. e. toward the light) and the openings are of such a size that their edges define a cone of view bounded (in the case of box 2|) by the lines 48-, 42-43 (in the sectional view shown in Figure 2), and the lines 44-45 and 46-41 (in the sectional view shown in Figure 3). At the position indicated by numeral 48 within box 2|, there is positioned a photo-electric cell mounted in any suitable manner not illustrated. Hence. any light falling within the angle of view defined by lines 48- and 42-43 (in the sectional view shown in Figure 2) and any light rail-- ing within the angle of view defined by the lines 44-45 and 46-41 (in the sectional view shown in Figure 3) is free to fall uniformly on any portion of the photo-electric cell cathode. Due to the finite width and height of the photo-electric cell 48 cathode, there is a marginal area around the cone of view in which any light will illuminate part but not all of the photo-electric cell. This marginal area lies between the lines 48-4I and 58-5I at the upper portion of Figure 2, and between the lines 42-43 and 52-53 at the lower portion of Figure 2. Similarly, there is a marginal area between the lines 46-41 and 56-51 at the right as shown in Figure 3 and between the lines 44-45 and 54-55 at the left as shown in Figure 3.

The photo-electric cell box 26 is identical with that shown at 2| except that it is inverted, the outer limits of the field of view of photo cell 59 of box 26 being illustrated by lines 68-6I and 62-63 in the section shown in Figure 2. As shown in Figure 3, the limits of View of all of the photo cells are identical for the direction shown in Figure 3, since the cells are mounted one over the other.

The photo-electric cell boxes 22, 23, 24, 25 and 26, are constructed similarly to box 2|, except that the baflling is so arranged as to allow cones of view defined as follows: For the photo-electrio cell 64 of box 22, the outer limitations of the cone of view are defined by lines 65-66 and 61-68. The cone of view of photo-electric cell 69 of box 23 is defined by lines 18-1I and 12-13. The cone of view of photo-electric cell 15 of box 24 is defined by lines 16-11 and 18-19. The cone of view of photo-electric cell of 88 of box 25 is defined by the line 8I-82 and 83-84.

It will be observed that the intermediate photoelectric cells 64, 69, 15 and 88 thus have cones of view extending throughout the total vertical area adjacent side wall I8, whereas photo-electric cells 48 and 59 of the bottom box 2| and top box 26 respectively have cones of view which do not reach throughout the entire side wall area I8. As will later be explained, all the photo-electric cells act in parallel and the cumulative effect of the arrangement shown is that alight source of given luminosity moving along any area bounded by walls I6, I1, I8 and I9, produces approximately the same net electrical response except in the small upper area between top wall I6 and the line 68-6I and the small lower area between bottom wall l1 and the line 52-53, these areas being considered as outside'the practical range of movement of the illuminated source. Thus a projectile moving throughout the range along any path normal to the plane of Figure 2 and through the right-hand portion of Figure 2 will serve to activate all or nearly all of the photo-electric cells, whereas a projectile within the upper and lower reaches and to the left (adjacent wall I9) of Figure 2 serves to activate only a select few of the cells. However, being closer to the cells, the degree of activation is greater and hence the response is approximately as much as when the projectile is to the far right as shown in Figure 2, and hence within the cone of view of a greater number of cells.

Figure 4 illustrates the front view of a representative one of the photo-electric cell housing. for example, that shown at 25. The horizontal baiiiing plates and 86 and vertical side baflling plates 81 and 88 cut oil stray light. Thus. the top horizontal baflling plates 85 are arranged so as to lie along the line 98-9I, the horizontal lower bafiiing plates 86 are arranged so that their edges lie along the line 92-93. The vertical barfiing plates 81 are arranged so that their edges lie along the line 44-45 (Figure 3) and the opposite vertical plates 88 have vertical edges lying along the line 46-41 shown in Figure 3. The corresponding bafiling plates of the remaining photo-electric cell boxes 2I, 22, 23 and 26 are arranged as shown in Figures 2 and 3. The entire interior of the photo-electric cell boxes, the baflles and the interior of the range are finished a dead black so as to absorb any stray light.

At each photo-electric cell station (of which there are two illustrated in Figure 1) there is an amplifier apparatus generally designated I88. These amplifiers are preferably identical and hence only one need be described. The amplifier shown in Figure 1 is provided with two power supply lines L1 and L2 and a signal line S1 and a reset line R1 for the amplifier at station I. The signal line is designated S2 and a' reset line is designated R2 for the amplifier at station 2. The signal lines S1 or S2 and the reset lines R1 or R2 are connected to the recorder generally designated I8I, illustrated in Figure l. The amplifier power supply lines L1 and L: of each amplifier are connected in parallel and are wired throughout the recorder so as to allow control of the entire system from the recorder as hereinafter explained.

In Figure 5 there is illustrated an exemplary diagram of an amplifier suitable for use at stations I or 2 or any other additional stations that may be used in the system. The alternating current feeders L1 and L2 of the amplifier are connected through a suitable fuse I83 to the primary I84 of a transformer generally de t d The transformer is provided with a secondary I86 of suitable voltage for supplying energy to the filament I 81 of a full-wave rectifier tube generally designated I I8, and another secondary I88 is connected across the plates I89 and III of the rectifier tube. The mid-point II2 of the transformer secondary I88 is connected by line II3 to line I I4, the latter being grounded at II5. Plates I89 and III being thus alternately negative thus feed the grounded negative line I I4 of the system. The filament I81 of the rectifier tube is connected through lines I I6 or II 1 to line H8 and thence through choke coil II9 to feeder I28, which constitutes the positive output of the rectifier circuit. Line II 8 is connected through condenser I2I to ground line H4 and line I28 is likewise connected through condenser I23 to a ground line. The two condensers I2I and I23 and the choke coil II9 thus serve as a filter network for smoothing out the pulsating current output of the rectifier. The transformer I 85, rectifier H8 and filter network II9-I2I-I23 thus constitute a direct current supply for the amplifier tubes of the system, and in Figure 5 these parts of the apparatus have been bracketed and so designated.

The system also includes a voltage regulator for the amplifier D. 0. supply, the regulator being over the bracket bearing that notation. To accomplish such regulation, the positive feeder I is connected directly to the plate I26 of thermionic tube generally designated I25. The filament I21 of tube I25 is connected through lines I28 and I29 to the secondary I30 of transformer generally designated I3 I, which is suitably energized by a primary winding I33. The mid-point I32 of the transformer secondary I30 is connected to line I35 which constitutes the regulated positive voltage feeder of the thermionic tube hereinafter described.

The regulator portion of the apparatus also includes the following components and circuits: From junction I36 on line II4 there extends a potentiometer circuit consisting of line I31, resistor I38, line I39, resistor I40 having an adjustable tap I4l, thence through line I42, resister I43, line I44 having junction I45 thereon, and thence through resistor I46 to junction I41 on line I 35. In parallel with the aforesaid potentiometer resistor, there is connected a circuit extending from junction I48 on line II4 through line I49 which is connected to the cold cathode I50 of a gas-filled regulator tube generally designated I5I, and thence through line I52, junction I53, line I54, junction I55, line I56, resistor I51, and line I58 to junction I59 on line I3 5. The regulator apparatus also includes a thermionic tube generally designated I60 having a cathode emitter I6I indirectly heated by filament I62 which is connected to any suitable filament voltage source. A first grid I63 is connected through line I64 to the adjustable tap I4I on resistor I40. A second grid I65 is connected through line I66 to junction I45 between resistors I43 and I46. A screen grid I61 is connected through line I68 to junction I55 between lines I54 and I56. The

- plate I10 of the tube I60 is connected through line I1I, through junction I12 and thence through resistor I13 to junction I14 on the regulated positive voltage feeder I35.

The operation of the voltage regulator portion of the system is as follows:

In the event an increase of voltage occurs on alternating current feeders L1 and L2, this is reflected as an increase of voltage eitherpermanent or transient in the D. 0. tube of full-wave rectifier tube IIO. Since the D. C. output of the rectifier tube I I0 is communicated to the positive voltage feeder I35 through the thermionic tube I25, it follows that the direct current potential applied to line I35 is dependent upon the degree of conductivity of the tube I25 which is in turn under control of its grid I24. The voltage upon grid I24 is determined by the relative values of resistor I13, the resistance from plate I10 to the cathode I6I of the tube I60. Whenever an increase of voltage occurs on line I20, it is desired to suppress this voltage in part before being applied to line I35, and in order to accomplish this function, the resistance of tube I25 is accordingly increased by making the grid I24 more negative than during conditions of normal voltage. This more negative condition of grid I24 is accomplished by reducing the resistance of tube I60. The reduction of resistance is accomplished by the fact that an increase of voltage at I35 causes practically no increase of voltage at junction I53 due to the characteristics of tube I5I (variable resistance characteristic). However, an increase of voltage at I35 does cause an increase of voltage at junction I4I. Thus the grid I63 is charged in a positive directionwith respect to cathode I6I causing a reduction in the resistance of tube I60; and as a result the grid I24 of tube I26 becomes relatively more negative than during normal operation, thus compensating the increase of voltage of the source. For the optimum operation of tube I60, it is desirable to connect the screen grid I65 to tap I45, and thereby maintain a somewhat positive voltage on grid I65. The suppresser grid I61 is maintained at the same potential as the cathode emitter I6I, via connection I 54.

Wherever there is available an alternating supply source, substantially free from voltage fiuctuation, the voltage regulator may be omitted and the output of rectifier IIO connected directly across feeders I I4--I35. However, in usual commercial installations the connection of even relatively small loads causes transient voltage fluctuations, and as these are sufficient to cause false indications, we have found it necessary to use the voltage regulator apparatus in order to have proper, fault-free functioning of this very sensitive apparatus.

There are six photo-electric cells, viz. 48, 59, 64, 69, 15 and illustrated in Figure 2, but for simplicity only two of the photo-electric cells are shown in Figure 5, these being cell numbers 48 and 15. It will be understood that the remaining photo-electric cells are connected in parallel. As illustrated in Figure 5, the cathodes 48C and 15C of the photo-electric cells are connected to the grounded negative line II4, whereas the anodes 48A and 15A are connected in parallel to photo-electric cell output line I15, which is in turn connected through a resistor I16 to a variable tap I11 on resistor I18. Resistor I18 is connected to ground line I I4 at junction I19, and the opposite end of the resistor is connected through line I 8I to junction 235 on line 234 and thence through line 234 to variable tap I99 on resistor I96. The thermionic tube I80 constitutes the second stage amplifier of the amplification and includes a cathode emitter I83 which is indirectly heated by filament I84, the filament being connected to any suitable source. The plate I86 of the tube I80 is connected through line I81, resistor I80 (having a variable tap I89) thence through resistor I90 and milliammeter I92 to the regulated positive feeder I35. From junction I95 on grounded negative feeder II4 there extends a potentiometer resistor generally designated I96 having variable taps I98, I99 and 200 thereon, the opposite end of resistor I96 being connected to junction 20I on the regulated positive feeder I35. Due to the voltage applied across the potentiometer resistor I96, there is accordingly established steady voltages at taps I98, I99 and 200. Tap I98 is connected through line 202 to the cathode emitter I83 of tube I80, and tap 200 is connected through line 203 to screen grid I85 of thermionic tube I80.

The first stage amplifier tube generally designated 206 includes a cathode emitter 201 which is indirectly heated by a suitable energized filament 208. The control grid 209 of the tube is connected through line 2 I 0, through junction 2I I and capacitor 2I2 to junction 2I3 on the photo-electric cell anode circuit I15. The cathode emitter 201 is connected by line 2I5 to junction 2I6, and thence through resistor 2 I1 having a variable tap 2! and through line 2l9 and resistor 220 to tap 22I on the grounded negative feeder H4. The suppresser grid 223 of tube 206 is connected by line 224 to junction 225 and thence through line 226 to Junction 2I8 on the cathode circuit. Line 228 is connected directly to the control grid I82 01 the second stage amplifier tube I88. Screen grid 228 of the tube 288 is connected through line 229 to junction 238, to which the plate 232 of the tube 286 is also connected by line 233. From junction 238 on the plate circuit there extends a line 234 which is connected at junction 235 to line I8I extending through resistor I18 to the negative feeder 4.

The output or the second stage amplifier is at junction I89 on resistor I88 from which extends a circuit leading through line 235 and resistor 236 and thence through line 231 to a control grid 238 of a gas-filled trigger tube generally designated 248. The trigger tube 248 includes a filament 24I which is suitably fed by alternating current through the filament feed wires 242 and 243. A resistor 244 is connected across the filament feed wires, and the mid-point 245 of the resistor is connected through line 246, having junction 241 thereon, to junction 248, and thence through line 249, junction 258, variable tap 25I and resistor 252 to ground line 259.

The output of trigger tube 248 is by way of a circuit extending from plate 253, line 254, junction 255, line 268, thence through normally closed contacts 26I and 262 of a reset relay 265, through line 263, through the grid of a signal relay 261, which is the operated instrumentality, then through line 268, normally closed, manually operated switch 269, line 218, through variable resistor 21I-212 to the positive terminal of a seprate rectifier and filter network 288-28 I'282. The output circuit continues from the negative output terminal 216 of the rectifier through line 211 to junction 258, thence through line 249, junction 248, line 248, resistor 244 to filament 2 of the tube 248. The plate of the trigger tube is connected to the filament by a circuit extending from junction 255 on the plate circuit, line 256, resistor 251, capacitor 258, through junction 248, line 246, resistor 244 to the filament 2.

The grid 238 oi. the trigger tube has a potential established by the output of tube I 88. The potential applied to the grid 238 of the trigger tube may have a definite value in reference to ground. The output circuit of the trigger tube is connected at junction 255 to variable tap 25I on resistor 252, it being noted that one end of resistor 252 is grounded to line 259 and that the other end of the resistor 252 is connected to the voltage regulated positive feeder I35 of the amplifier system. Thus, the output of second stage amplifier tube I88 establishes a potential gradient from plate I86, through resistor I88, resistor I98, thence to the voltage regulated positive feeder I35, and then the latter is connected through resistor 252 to the grounded negative of the system. Accordingly, as the voltage of tap I89 varies, grid 238 of the trigger tube has a definite voltage of reference with respect to the filament 2 of the trigger tube.

Operation of station amplifier grounded negative supply line II4. From intermediate voltage tap I88 on the potentiometer resistor I86 a circuit is established through line 234 to plate 232 and thence to cathode 281 (of tube 288), and through resistor 2", line 2l8, and resistor 228 to tap 22I on the grounded negative feeder H4. The current flowing in this circuit establishes an intermediate positive potential at tap 2I8 on resistor 2, and this is communicated through a resistor 2 I4 to junction 2| I on the grid connection 2I8 or tube 286, thereby establishing positive potential on the control grid 289 o! the ube.

An intermediate positive potential is also communicated from cathode 281 of the first stage amplifier to the grid I82 of the second stage amplifier I88, and the latter tube is conductive. This condition of both tubes being conductive continues so long as the photocells are maintained at a. given degree of darkness.

When light falls upon the photo-electric cells they become somewhat conductive, and accordingly serve to drain ofi the electrical charge normally accumulated on line 2I8, the drain being through the circuit extending from junction 2| I, capacitor 2 I 2 to junction 2 I3, and thence through the photo-electric cell (or cells) to the grounded negative supply line H4. The consequent decrease in positive voltage of grid 288 of tube 286 renders tube 286 less conductive and as a result, less current fiows through the plate circuit of the tube. As previously explained, the plate circuit of tube 286 traverses resistor 2", and the normal plate current fiowing when the photocells are dark establishes the grid potential of the amplifier. Hence, when the photocells are illuminated the first efiect is to reduce the plate current through tube 286, and as this occurs, tap 2I8 of resistor 2I1 (which is in the plate circuit) tends to shift to the negative. As a result, there is less tendency, for the positive potential of grid 289 to be re-establlshed and the decrease in conductivity of the tube 286 is hence cumulatively effective in further decreasing the conductivity of the tube once the initiating impulse is received from the photoelectric cells.

Since the grid I82 of the second stage amplifier tube I88 is connected directly to the cathode of tube 286, any decrease in conductivity through tube 286 is immediately reflected on tube I88 which likewise becomes less conductive. The plate circuit of tube I88 extends from tap 28I on the positive feeder I35 through the milliammeter I92, resistors I98 and I88, line I81, plate I86, through the tube I88 to cathode I83, through line 282 to tap I98 on the resistor I96, and thence through the resistor to tap I on the grounded negative supply line I I4. The decrease in conductivity of tube I88 (which is equivalent to an increase of resistance of the tube) causes the potential of tap I89 to become more positive and this positive impulse is communicated directly through lines 235, resistor 236 and line 231 to the grid 238 of the trigger tube '248. The impulse causes the latter tube to trigger off and begin to conduct.

The operation circuit of the trigger tube extends from the positive terminal 215 (of separate rectifier and filter 288-28I-282) through resistor 212, terminal 2', line 218, normally closed manual reset switch 269, line 268, the coil grid of signal relay 261, line 263, normally closed contacts 262-26I, of the reset relay 265, line 268, junction 255, line 254, to plate 253, thence through the trigger tube 248 to filament 2, through resistor 244 to the mid-point tap 245,

9 thence through line 246 to junction 248, line 249, junction 250, line 211 to negative terminal 215 of the rectifier 230-28 |282.

The circuit thus established through the trigger tube 240 causes the energization of relay 261 which closes its movable contact 280 upon its fixed contact 281, thus establishing a circuit from the alternating current feeder L2, through the then closed contacts 280 and 23l to the signal line S1 which serves to actuate the recorder as hereinafter explained. The trigger tube 240 continues to conduct once ionization is established in the tube, and therefore in order to interrupt the circuit, there are provided normally closed contacts 26l-262 of the reset relay generally designated 265. For opening these contacts a circuit is established at the recorder station, as hereinafter explained, from the alternating current feeder Lz, at the recorder station, through reset line R (or R2) to the coil of relay 265 and thence through line 284 to line I at the station amplifier.

Upon energization of reset relay coil 265, contacts 26| and 262 are sep"ated, th'us interrupting the output circuit of the trigger tube 240. This allows relay 261 to become deenergized. If desired, the circuit through the trigger tube may be interrupted by manually operating the normally closed switch 269.

In order to calibrate the amplifier apparatus, a voltmeter 288 is provided between lines 211 and the ground line 259. A millivoltmeter 290 is connected across lines 246 and 235 and a milliammeter I92 is provided in the plate circuit of tube i 30. By means of these instruments and the various adjustments provided, the apparatus :may be adjusted for operation under any desired de-' gree of light change on the photocells.

Recorder and indicator The overall sensitivity of the system can also be varied by changing the voltage applied to the photocells, by varying the adjustment of tap I11 von resistor I18. A potential of 80 volts at point 290 and a manually operated control switch 29l.

The lines L1 and L2 extend through the recorder and connections are made from the left ends of L1 and L2 of Figure 6, to each of the photo-electric cell station amplifiers as illustrated in Figure 1. Accordingly, fuse 290 and switch 29l serve to control the entire system,

In the indicator and recorder mechanism there is provided a transformer generally designated 292, having a primary winding 293 connected by means of lines 294 and 295 to the alternating current feeders L1 and L2 respectively. The transformer is provided with a secondary winding 296 which is connected to line 295 at junction 291, and hence through line 295 to alternating current feeder L2. The opposite terminal of winding 296 is connected to a secondary feeder 298 which serves to supply low voltage alternating current potential to the various portions of the apparatus. The transformer is also provided with secondary winding 300 which is connected through lines 3M and 302 to the alternating current terminals of the full-wave rectifier generally designated 304. The positive direct current terminals of the rectifier 304 is connected by line 305 to junction 306 on the grounded alternating current feeder L1. The negative terminal of the rectifier 304 is connected to line 301 which serves as a direct current supply line to various portions of the apparatus.

The recorder apparatus includes a tape drive motor generally designated 3I0, one terminal of which is connected by means of line 3 to junction 3I2 on the alternating current feeder La. The opposite terminal of the tape drive motor 310 is connected by means of line 3|3 to stationary contact 3 of a slow release relay generally designated 3|5, A mechanical connection 340-extends from the motor 3l0 to a tape drive roll 342 and may include any suitable gearing so that the tape drive roll 342 is rotated at a desired slow or fast rate when the tape drive motor 3| 0 is operated. Referring to Figure '1, the tape drive roll 342 serves to pull tape 343 from the tape supply roll 344. Tension is maintained upon the tape by means of an idler roller 345 which is held in contact with the motor-driven tape-drive roll 342 by means of its mounting on arm 346. The arm 346 is pivoted at 341 and a spring 348 is attached thereto so as to cause the arm 346 to be pulled against the motor-driven tape-drive roll 342, and thus any desired tension is maintained. The arm 346 is provided with a chute 349 along which the marked tape record slides from the machine.

The apparatus shown in Figure 7 also includes an illustration of the condensers generally designated 292 and several elements of the rectifier generally designated 304. Above the tape roll there are provided one or more recorded solenoids generally designated 310 having windings 31!, one such recorder solenoid corresponding to each photo-electric station. The core of the solenoid includes an iron portion 312 and a brass stylus end 313, the core being spring mounted by means of spring 314 which is attached to the screw adjustment knob 315. Whenever the solenoid 310 is energized, the point of the stylus is brought into contact with the tape, thereby making a mark on the tape.

The slow-release relay 315 is provided with a movable contact 3i6 which is connected through junction 3l1 and line 3|8 to junction 3l9 on the grounded A, C. and positive D. C. feeder L1. From junction 3l1 there extends line 320 which is connected at junction 32I to the winding of relay 3 i 5 and also to one terminal of a condenser 323. The opposite terminals of winding of the relay 3 I 5 and condenser 323 are connected at junction 324 and thence through line 325 to contact 326 of the vibrator relay generall designated 330. The slow release relay 3| 5 is capable of instantaneous pickup, but will remain energized for a period of A; to 1 second after energization ceases, depending upon adjustment.

The vibrator relay 330 is provided with two aciive spring-mounted contacts 326 and 321, and inactive spring-mounted contact 328. A vibrator contact 329 is weighted at its outer end as shown at 33L In the condition of rest, the weighted, springy contact 329 is in engagement with the active contact 321, but during such condition of rest the contact 326 is separated slightly from contact 321. The contact 328 is not connected in the circuits shown, but serves as a mechanical countei'part or contact 321 so as not to de-tune' 333 to junction 334 from which connection is made through the wi'nding of the vibrator relay 330 and through a condenser 336 in parallel, to Junction 331.;and thence through line 335 to junction 338. The springy, weighted contact 329 of the vibrator relay is connected directly to the "negative output line 30! or the rectifier. From junction 338 connections are made in parallel toeach of the recorder control relays corresponding to'each recorder station in the system.

A recorder control relay is provided for each photocell amplifier station and hence there are two recorder control relays in the herein illus-- trated system. Thus there are provided a recorder control relay 350 (corresponding to station I) and a similar recorder control relay 380 (corresponding to station 2).

Relay 350 is provided with contacts 35!, 353, and 355 which cooperate respectively with movable contacts 352, 354 and 356, the movable contacts being out of engagement with their corresponding stationary contacts when the relay is deenergized. The winding 251 of the rela is connected to line 359 at contact 352 and to signal line S1 extending to the photo-electric cell amplifier station number I, the circuit through coil 35! thus being from L1 at the recorder (Figure 6) thence through line 359, to contact 352, thence through winding 35! to line S1 which continues to the amplifier station (Figure 5) through contacts 280 and 28! (when closed in response to a signal) and to feeder L: at the amplifier of station I.

When coil 330 is energized reed 329 is drawn toward the coil, forcing contact 32'! against contact 326. When the circuit through the coil is broken reed 329 is released and continues to vibrate. Snubbing of the reed 329 is prevented by the positioning of the contacts as shown; for example, in the event the next impulse through the coil occurs when the position of reed 329 is out of contact with contact 328, no circuit is established through the coil, and reed 329 hence continues to vibrate.

The energization of coil 351 01' the recorder control relay 350 causes the simultaneous closure or each of its movable-contacts 352, 354 and 356 upon the stationary contacts 35!, 353 and 355 respectively. The closure of contact 352 upon contact 35! establishes a circuit from the negative terminal of the full wave rectifier 304 through line 30'! to vibrating reed contact 329, which is then closed against contact 321, and thence through line 333, through the coil of the vibrator relay 330, line 335, junction 338, line 339, contacts 35 and 352, line 359, junction 358, feeder L1, Junction 306 andline 305 to th positive terminal of the full wave rectifier. The vibrator relay is hence energized and reed 329 begins to vibrate. As will be explained, this circuit through contacts 35!352 remains closed only a shorttime but I reed 329 continues to vibrate for a period of time after the direct current circuit through the coil 01' relay 330 has been interrupted.

The vibration of reed 329 causes the energization of the slow release relay 3l5 through a circuit beginning at the positive terminal of the full wave rectifier 304, through line 305, junction 306, feeder L1, junction 3|9, line 3l8, junction 3 !1, line 320, junction 32!, thence through the coil of slow release relay 3| 5, junction 324, line 325, to contact 326, which is in engagement with contact 32! when the latter is deflected due to the engagement of the vibrating reed contacts 329 the e n 12 The circuit thus extends through contact 326 and contact 32! to the vibrating reed 329 and thence through line 30! to the negative terminal of the full wave rectifier 304. Direct current impulses are accordingly sent through the coil of slow re- I lease relay 3l5 as long as relay 330 vibrates, and the movable contact MB of relay 3l5 accordingly engages stationary contact 3. The slow release relay contacts 3!4-3l6 remain closed for %-1 second after energization of the coil of the relay ceases, and while closed a circuit is maintained from alternating current feeder Lrthrough line 3l8 to junction 3H, thence through closed contacts 3!6 and 3 l4, line 3l3, through the tape-drive motor 3!0 andline 3!! to junction N2 of the alternating current feeder L2. The energization of the tape-drive motor causes the rotation of the tape-drive roll 342 and the recording tape 344 is therefore rolled through the machine, either slowly or quickly, according to the design of the I machine.

The energization of the recorder control relay 350 also establishes a circuit through the station recorder 310-! corresponding to station No. I as follows: From alternating current feeder L2 through line 360, junction 36!, line 362, then closed contacts 355 and 356, line 363, through the coil of station recorder solenoid 310--!, line 298 to one terminal of the transformer secondar 296, through the transformer secondary to junction 29'! and thence through the line 295 to alternating current feeder L2. The station recorder solenoid 310-! causes its solenoid 312-! to be drawn downwardly until the stylus point 3'!3l is brought into engagement with the tape 344. This causes a dot impression to be formed on the tape, for the station recorder solenoid is immediately withdrawn due to the deenergization of recorder control relay 350, as will be explained. I

The recorder control relay 350 remains energized until the trigger tube output circuit of its corresponding amplifier is broken, this being accomplished by energizing the reset relay 265 of the amplifier station through contacts 353-354 of relay 350 as follows: From alternating current feeder L2 through line 360, junction 364, line 365, then closed contacts 353 and 354 to reset line R1 which extends to the reset relay 265 of the photocell station amplifier for station No. I (Figure 5), thence through the relay 265 and through line 284 to alternating current feeder L1. The energization of relay 265 causes contact 26! to be broken from contact 262, thus breaking the trigger tube output circuit through the signal relay 261 whereupon contact 280 of relay 26'! moves out of engagement with its co-- operating contact 28! accordingly de-energizing the recorder control relay 350 (of Figure 6). The entire sequence which involves initially the energization of the signal relay 261, the consequentenergization of recorder control relay 350 (which sets the vibrator relay- 330 into operation, and thus causes the slow release to pick up and the tape drive motor to start together with the operation of the station recorder 310-! of station- No. I) and the operation of the reset relay 265- sion that it is not audibly distinguishable.-

Therefore a light impulse upon the photocell, if amplified, causes the operation or the relays in sequence, thus causing the marking of the tape j tion of the relay at Station No. I. It will be noted that in this instance also the signal is received from the photocell station amplifier of station No. 2 by way of signal line S2 which communicates the impulse to the coil of recorder control relay 388 for station No. 2. This causes the closure of movable contacts 382, 384 and 386- upon stationary contacts 38I, 383 and 365 re-' spectively. The closure of contact 382 upon con-- tact 38I establishes a circuit to the vibrator control relay 338 in the same manner as that estab-- lished by contacts 35| and 352 of relay 358, and the vibrator control relay in turn causes the operation of slow release relay 3I5 and the operation or tape drive motor 3I8. The closure of contact 384 upon contact 383 establishes a circuit to the reset relay 265 of the photocell station amplifier corresponding to station No, 2, and the latter in turn causes the de-energization of the trigger tube output circuit and consequent de-energization of the signal relay 261 of station No. 2, which in turn opens the circuit through the recorder control relay of station No. 2. The closure of contact 386 upon contact 385 establishes a circuit through the station re-' corder 3182 corresponding to station No. 2 which operates the stylus 3132 for marking the tape, this being exactly analogous to the operation discussed above which occurred when the contacts 355 and 356 are closed by the energization of relay 358 and station No. I.

Thus, assuming that the illustrated system is utilized for the testing of projectiles, the movement of the projectile alon path |I-I2 of Figure 1 past station No. I will cause the photocells of station No. I to be activated, with con-' sequent movement of stylus 313--I corresponding to the station No. I into contact with tape 344. The movement of the projectile past station No. 2 will cause the photocells of station No. 2 to be activated, with consequent movement of stylus 313-2 corresponding to the station No. 2 recorder, into contact with tape 344. The movement of the projectiles will thus cause two dots to be marked upon the tape 344.

Where the tape-drive motor is arranged to move the tape relatively slowly, the two dots caused by stylus 313-I and 313-2 will be nearly opposite each other because the tape, under such conditions will not move an appreciable distance during the time interval required for the movement of projectile from station I to station 2. The apparatus thus records the fact that the projectiles are moved past stations I and 2 and that a given condition of illumination of the pro jectile exists during the time of such movement.

By designing the apparatus for rapid tape move-- ment, the dots are spaced apart and a measure of the projectile velocity is afiorded.

Specific examples of photocell station amplifier constants for recording the performance of tracer bullets.

14 It will be understood, of course, that other specific designs of the apparatus are equal within the purview of the invention and that this example must therefore be considered merely as illustra tive Photo-electric cells:

First stage amplifier 286 Second stage amplifier I88 8V6 Trigger tube 248 287A Cold cathode tube I5I VR150 Amplifier I68 BSJ'I Thermionic tube I25 61346 Rectifiers H8 and 28I 5Z3 Resistor 228 Zmegohms Resistors I16 and 2I4 60 megohms Resistor 2 I1 1 megohm Resistors I18, I38 and 6.. 10,000 ohms Resistor I96 25,000 ohms, watts Resistor I48 15,000 ohms Resistor I43 20,000 ohms Resistor I51 75,000 ohms Resistor I13 /2 megohm Resistor I88 10,000 ohms Resistor I98 2,500 ohms Resistor .236 100,000 ohms Resistor 251 500 ohms Resistors 25I and 212 25,000 ohms Condensers I2I, I23 (and the condensers of filter network 282) i 8microfarads Condenser 256 /2 microtarad Condenser 2I2 .00025 microfarad A photocell amplifier apparatus having the foregoing constants when properly adjusted is sufficiently sensitive to cause actuation of the signal relay 261 and consequent operation of the recorder when a piece of chalk or a yellow lead pencil is thrown through the photocell frame (Figure 2), and is unfailingly responsive to even the slightest illumination of a tracer bullet. Widely varying line voltage fluctuations do not cause false actuation of the signal relay 261.

When using a device for the recording of tracer bullets, it is frequently desirable to include in the recorder apparatus a recorder control relay, together with its station recorder and associated contacts, supports, etc., for making a record of the firing of the gun from which the tracer bullet is shot. The recorder control relay under such circumstances is energized by a micro switch positioned behind the gun so as to be closed instantaneously by the recoil of the gun. This serves to energize the recorder control relay of the firing station and as a result the corresponding station recorder places a mark on the record tape, the vibrator relay 330 is energized and the tape motor 3I8 is started. In the event the tracer bullet fails entirely and provides no illumination during its passage through the firing range, the recorder nevertheless shows that the bullet was fired, thus providing a record in the event of complete failure of the tracer charge in the bullet.

It is also desirable to provide in the apparatus a bulb connected across the terminals of the recorder control relay for each station as illustrated at 390 and 39L In this way a visual indication of the operation of the apparatus is provided, in addition to the record made on the record tape.

Many obvious variations will occur to those skilled in the art. Thus, the apparatus may be utilized for recording the movement of packages past a given point, for the passage of very small plurality of photocells connected in parallel, a

housing for each photocell having a baflie therein-for determining the angle of view of said each photocell, said photocell housings being arranged with respect to each other that the angle of view as determined -by said baiile overlaps at least partialhr the angle of view of at least one ad- ,iacent cell. I

2. A photo-electric apparatus comprising a plurality of photocells connected in parallel, a housing for each photocellhaving a baflie, therein for determining the angle of view of said each photocell, said photocell housings being arranged with respect to each other that the angle of view as determined by said baflie overlaps at least energized by one of said sources and trigger tube partially the angle of view of at least one adjacent cell when seen from one elevation and completely overlaps the angle of view of said adjacent cell when seen from an elevation at right angles thereto.

3. A photo-electric apparatus comprising a plurality of photocells connected in parallel, each cell being in a housing, said housings being positioned adjacent each other, each housing being provided with a battle defining the angle of view of the cell in said housing, the baiiles being of a size and so positioned that a plurality of adjacent cells view overlapping vertical projected areas adjacent the cell housings.

.4. A photo-electric apparatus comprising an amplifier, having a cathode, grid and plate, a circuit for the amplifier extending from a source of positive potential, thence through the amplifier plate and cathode and thence through a re:- sistor to the negative of said source, a grid charging circuit extending from an intermediate point on said resistor to said grid, and a photocell connected to said negative of said source and connected to said grid through a condenser.

5. A photo-electric apparatus comprising a photocell, amplifier means connected thereto for amplifying impulses from said cell and a trigger tube having a control grid connected to the amplifierand a. cathode-plate output circuit, relay means connected to said trigger tube output cir cult, and electromagnetic circuit control means connected to said relay means and responsive to the fiow of current therethrough for interrupting the cathode-plate ou put circuit of the trigger tube.

6. A sensitive photo-electric apparatus comprising a photocell, an amplifier having a cathode, grid and plate, a rectifier adapted to be connected to a source of alternating current for providing a unidirectional voltage source to energize said photocell and amplifier, said photocell being connected to said source and to the grid and said cathode and plate connected to the source and to an output circuit, and a thermionic voltage regulator connected between the rectifier and the photocell and amplifier circuits for preventing 16 false operation of the fluctuations of said alternating current'source.

7. A photocell amplifier apparatus comprising a photocell, an amplifier having input and output circuits, the input circuit being connected to the photocell so as to of said amplifier, and separate rectifiers adapted to be connected to an alternating current source for providing separate unidirectional voltage sources, the amplifier being, connected to and being connected to and energized from said other source.

8. A photocell amplifier apparatus comprising a. photocelhan amplifier having input and output circuits, the input circuit being connected to the photocell so as to be responsive thereto, a grid controlled trigger tube connected to the output of said amplifier, separate rectifiers adapted to be connected to an alternating current source for providing separate unidirectional voltage sources, the amplifier being connected to and energized by one of said sources and trigger tube being connected to and energized by the other of said sources, and a thermionic voltage regulator connected between the amplifier and the rectifier power source supplying power to said amplifier.

9. A photo-electric apparatus comprising an elongated housing, open along one side, a plurality of partitions extending across the housing and positioned so as to separate it into a plurality oi. compartments each open on the open side of the housing, photocells in each compartment.

spwed away from the open side thereof, said photocells being electrically connected together, the location of the photocells of successive compartments being varied from one compartment to the next in a direction longitudinally of the housing so as to expose the cells in each compartment to substantially overlapping fields of view.

10. The apparatus of claim 9 further characterized in that said compartments include baflies spaced between the open side of each compartment and the photocell with it so as to define the field of view of each cell and shield the cell from light outside the fields of view so defined.

HARRY WILLIAM HOFFMAN.

REFERENCES CITED The following references file of this patent:

UNITED STATES PATENTS are of record in the latter in response to voltage be responsive thereto. a grid 1 controlled trigger tube connected to the output y 

